26. Anatomy and physiology of and anorectum

Question 1

Where does the GI tract arise from?

Answer 1

From the endoderm of the embryo in week 3 from the buccopharyngeal membrane to the cloacal membrane
Rememeber ther is the endoderm, mesoderm and the neural crest

Question 2

What are the subdivisions of the GI tract and what is their blood supply?

Answer 2

Foregut - coeliac trunk (T12)
Midgut - Superior mesenteric artery (L1)
Hindgut - Inferior mesenteric artery (L3)

Question 3

Where are fluids and electrolytes absorbed in the GI tract?

Answer 3

Small intestine - some water, NaCl in the ileum

Large intestine - 90% of remaining volume

Question 4

What is meant by diarrhoea?

Answer 4

Excessive water secretion in the faeces

Question 5

What is meant by constipation?

Answer 5

Decreased water secretion in the faeces

Question 6

What are the pelvic floor muscles?

Answer 6

Levator ani muscles - iliococcygeus, pubococcygeus, ischiococcygeus

Puborectalis - the main one when it comes to the pelvic floor

Question 7

Are the anal sphincters voluntary or involuntary?

Answer 7

Internal anal sphincter - involuntary muscle

External anal sphincter - voluntary muscle - this is the one that we need to stimulate when we want to pass stool

Question 8

Briefly describe puborectalis

Answer 8

Striated muscle of the pelvic floor
Forms a u-shape at the back of the pubic symphysis
Surrounds the rectum, vagina and the urethra
Creates the anorectal angle

Question 9

What is the innervation to the anorectum?

Answer 9

Sacral nerves S2, 3, 4 via the pudendal nerve - this is a paired nerve

Question 10

What are the branches of the pudendal nerve?

Answer 10

Branches to the inferior and exterior rectal nerves

Inferior rectal nerves - perineal nerve, dorsal nerve of the penis and of the clitoris

Question 11

What is meant by faecal continence?

Answer 11

Maintenance of faeces within the rectum

Question 12

How is faecal continence maintained?

Answer 12

Maintained by the internal and external anal sphincters and the puborectalis muscle

Retaining stool in the rectum is known as resevoir continence

Question 13

What are the individual roles of the different anal sphincters?

Answer 13

IAS - responsible for the closure of the rectum and maintains the resting pressure

EAS - responsible for the contraction of the anus and the pressure during this contraction

Question 14

What is RAIR?

Answer 14

Rectoanal inhibitory reflex
Enables you to relax your sphincter to be able to empty the rectum
Progressive anal filling initiates this reflex

Question 15

What is the closing reflex?

Answer 15

After the last bolus of food is passed - reflex of the EAS

Voluntary contraction also aids closure of the EAS

Question 16

What is meant by faecal incontinence?

Answer 16

Involuntary passage of rectal content - gas or stool

Is a source of major embarrassment of the sufferer

Question 17

What is meant by passive incontinence?

Answer 17

When the internal anal sphincter is not working

Patient has no awareness of passing stools until they actually then feel it i.e. in their pants

Question 18

What is meant by urge incontinence?

Answer 18

When the external anal sphincter is not working

Patient feels the immediate urgency to pass stool but does not make it to the toilet in time